Multiple unit high-frequency amplifier



Aug. 30, 1932. s, LQEwE 1,875,057-

MULTIPLE UNIT HIGH FREQUENCY AMPLIFIER Filed Sept. 17, 1925 4o Fm 46 "g922 43 L 49 /n venior:

Patented Aug. so, less srneivrunn LoEwE;

0.? BER-LIE, GERMANY, ASSIGNOE TO RADIO CORPORATION OF AMERICA, ACQRPORA'EEON OF'IDELAWAR-E MULTIPLE UNIT HIGH-FREQUENCY AMPLIFIERApplication filed September 17, 1925, Serial No. 56,953, and in GermanySeptember 23, 1924.

It has been found, that the problem of aperiodic high -frequencyamplification, where the number of periods exceeds 500,000 per second,becomes with the use of vacuum tubes more and more dificult as the rateof frequency increases (see Barkhausens Elektronenrbhren Leipzig 1923,page 92). For these higlrfrequencies, iowever, it is absolutelynecessary to have high frequency amplifiers, because on the one hand,short wave lengths are generally used forbroadcasting purposes, and onthe other hand, because short wave lengths have proved especiallysuitable for long distancetransrnission.

The object of this invention is to provide an aperiodic high-frequencyamplifier, which is effective up to very high frequencies. Repeatedtests have proved that the ordinary capacity-resistance connection forhighefrequency amplifiers is well suited for this purpose, provided twofactors have not been left out of consideration, namely the capacitiesbetween the circuit elements and the capacities in the interior of thetube should be kept as low as possible. Barkhausen has already pointedout this necessity.

On thevother hand experience has proved that'the resistances. heretoforeused for the purpose will cause certain disturbing influences, whichrender them unsuitable for use in high-frequency amplifiers. They showcertain properties, which may be termed residual voltage effects. Theseproperties are characterized bythe fact that as in the case ofcondensers and storage batteries after a current has passed through sucha resistance, a certain residual voltage will remain, and will only veryslowly flow 05. It is quite easy to observe this surplus voltage evenafter. the lapse of several seconds. If a resistance showing theseresidual properties is traversedby high frequency currents, it will actlike a capacity, that is its effective resistance will decrease with theincrease of the frequency.-

The problem forming the basis for the in-- frequencies.

1 shall further describe my invention with the aid of the accompanyingdrawing in which: 7

Figure 1 is a wiring diagram of a three stage amplification system.

Figure 2 is an evacuated vessel in which, according to my invention,most of the three sta e amplification system shown in Figure 1 has beenincorporated.

Figure 8 is a modification thereof.

Fig. 1 represents a three-stage high-frequency amplifier produced inconformity with the invention. The tubes used are standard tubes, butwithout bases. These tubes are indicated by the reference numerals 1, 2and 8. The heating filaments 4i, 5 and 6 may, for instance be heated in.series by a battery 7. The energy to be ampli lied is applied betweenthe terminal 8 connected to the negative side of filament 4 and theterminal 21 connected to first grid 9. The first anode i0 is connectedto the positive pole of a battery 12 by way of a bus for suppl ingpositive potential and an ohmic resistance 11 of high resistance valueand free of all residual effects. Furthermore the first anode 10 isconnected with the grid 18 of the second tube by way of a highly in-Sula-ted condenser 12. The anode 14 of the second valve is alsoconnected, by way of Y the positive and an ohmic resistance having ahigh resistance value and being free are further connected, by way of abus for stage is similarly connected to the third.

supplying negative potential and like resistances 18 and 19, with thenegative battery pole. The first tube or stage is connected. to

the second by an impedance coupling com-' prising the highresistances'll and '18, and the condenser 12, and the second tube or Theamplified high-frequency voltage may thus be taken off between theterminals It is possible, for instance, toconnect a tuned frame antennabetween the terminals 8 and 21, and also by inserting a coil or othersuit 1 able. coupling means between the terminals 20',ithe amplifiedhigh frequency voltage may be appliedto a' vacuum tube detector orcrystal detector circuit followed by one or morestages of low-frequencyamplification. It has .been'found, that it is possible with the help. ofsuch resistances,-whic'h are free of any residual efifect in the anodecircuit, as well as 1n the grid connections, and bytWOlfling 'the'production of-capaclties 1n the tube base, tofproduce properly operatinghighfrequency amplifiers up to wave lengths of 150 meters. I

, The high-frequency amplifier described above will still possess acomparativelylarge capacity between the several elements of the circuit.{In orderto reducethis capacity to a 'minimunnthe following steps havebeen taken by the inventor H The multiple high-frequency amplifiersystem is enclosed within a tube, the resist ances in the grid circuitand the transfer capacities being also preferably mounted withinsaidtube. For this purpose, the resistances in the grid circuit and thecapacities 12 and 16' can be enclosed in special tubes, or if necessaryin vacuum tubes.

Fig.2 shows as an example atriple or three stage amplifier, constructedaccording to this invention. I

In a glass frame 22 the filament 24 adapted to be heated to incandesenceis held in position by the insertion of a tungsten spring 23. Thethreegrid and anode sets constitutin g the three stages are, as shown in thisfigurefarranged either on the side, or cylin drically round the glowingfilament. On the framethere is further mounteda collecting wire ornegative bus 25,.connected with the negative pole of the heatedfilament. Similarly the frame carries a rod or positive bus 26'connected with the'positive battery pole;

The first grid is carried, for instance, through the glassbulb at 27 andthe positive terrninal of the filament iscarried through at 28.

The first anode is'connected by a resistance 11, which is free ofresidual effects, to the positive collecting wire or bus, and by Way ofacapacity 12 which is preferably enclosed within an air-tight space tothe second grid 13. The second grid, if desired, can

also be connected by Way of a resistance 18,

which'is absolutely free of residual effects,

to the negative collecting wire. The second a condensor 16 which isenclosed in ava'cuuin to the third grid 17. The third anode is led outthrough the stem, while the third 'grid;

can-be connected by way of a resistance 19 of the same character to thenegative collecting wire 25. The surrounding glass bulb 29 encloses thewhole apparatus airtight and it has altogether five sealing-inpoints,-viz.,

two for the filament ends, one for'the' first L gridyone for thethird'anode, and one-for the positive collecting wire'or' bus. By meansj of this arrangement, it. is possible to reduce theeffect of theinjurious capacities tosuchi an extent that amplification ofhigh'frequen-j cies up to 10,000,000cycles" can be'obtained,

further improvementcan be obtained by f the use of insulated" grids. Bythe use'of] such grids, that is, a grid thesurfaceof? which is suitablyscreened against the reg ception 'offelectrons, as for instance by theinterposition of mica sheets or by coating the grid with borax orporcelain. enamel, the. otherwise necessary blockcondensers 12' and 16can bedispensedwith, as well as the re sistances 18 and 19 in the gridcircuits which, 1

are necessary in most cases.

An example of the construction of the sys} term with insulated gridsfisshown in FigI'Si' The grids in this case are designed as controlelectrodes, and are not fixed between; plate and cathode, .but beyondthe spacelbe-Q tween plate and cathode.

are well known. mounted as shownin Fig; 2. The'first anod The effect andprinciples of this arrangement as amplifier The heating filament is,

40fissituated in the left hand top corner, and. the first control. grid41 in the right hand} topcorner'; Itis carried out of the glass bulbjust like'the filament terminals. Mica plates are interposed betweeneach of the con- I J trol electrodes and the filament, said plates beingeither, fastenedlon to the control electrodes, or kept freely insuspension by means of small brackets positioned in the space be-Itweenfilament andcontr'ol electrode. For

the three stage'sithese mica plates-are designated respectively 42, 43,44. Fromthe-first anode the circuit leads by way of a=resist= ance 45which is free from residualefiectsi 1 to the'positiv'e collecting wire26', which is also sealed into the 'foot" of' the bulb. The

second stage is so arranged that the sec d i A control grid 46 issituated on the same-sideas the first anode.

It is connected with the latter by means of a wire, but screened fromthe filament by an interposed mica plate .43. The second anode 4:7 isconnected, by Way of a resistance 48, free of residual effects, to thepositive collecting wire 26. The third control grid i9 is placed on thesame side of the filament as the second anode and this grid is alsoscreened from the filament by an interposed mica plate 44, and connectedconductively with the second anode by a wire. The third anode isseparately supported and led out through the stem of the glass bulb.

In the manner described it will be possible to build high-frequencyamplifying sets, hardly larger than the plain amplifying tubes used atpresent, and yet many times more effective.

.My means of the last-described construction an efiective amplificationof the highest existing frequencies will be made possible. It is ofcourse not necessary to confine oneself to a three stage construction,since a still larger number of similarly constructed stages may be used.

It is further of great importance that the first stages havecomparatively short lengths of the anode and the grid, as the currentsin the first amplifying stages are very weak. Only the subsequent stageshave larger anode and control surfaces to correspond with the increaseof the currents to be carried by the apparatus.

Frequently the problem may arise to construct such sets in a form whichwill permit of a low current consumption. If filaments are used whichare coated with an oxide covering, there will be no difference in thedesign used for tungsten filaments.

If, however, an economy in heating current by the atomization ofmagnesium or similar metals in vacuum is desired, care must be takenthat the deposits of metal thus produced will not provide any conductivepath between the different parts, which should be insulated from eachother. The inventor has found that the formation of a conductive depositbetween two points which should be kept insulated from each other can beavoided by protecting the points in question by means of a screen eitherof glass, metal, or mica, which is placed in front of the places to beprotected against such deposits. Protective screens of this kind areused wherever it is necessary to maintain a high insulation. The depositin this case settles on the screen, and the protected parts, which mustremain insulated, will remain free of such deposits. The evacuation ofthese systems is best done by placing the entire tube on the pump in ahigh frequency eddy cur rent field.

For mounting the blocking condensers in the vacuumtubes according toFig. 2, it. will.

be preferable to enclose the condensers separately in airtight glasstubes. This method.

evacuate the condenser itself. For example,

two copper foils separated by a strip of mica may be placed within aglass tube, said foils I being rolled into a small coil. The two ends ofthe glass tube must be sealed, and the two leads carried out-side. Thistube may be freed of air, but it is quite sufficient to seal in thecondenser perfectly airtight. Similarly, the degassing of the high ohmicresistances may be dispensed with by sealing them, if possible, undervacuum, into glass tubes. Condensers, or resistances, enclosed in avacuum tube in the manner described above will behave exactly like anyparts of the surrounding glass surface, considered from avacuum-technical point of view.

I claim:

1. A. vacuum tube adapted for multistage amplification, comprising anevacuated envelope, a plurality of stages contained therein, a singlefilament common to all the stages, a control electrode and a plateelectrode for each stage, impedance coupling between successive stages,a collecting element, and a high resistance element connecting thecontrol electrode of the last stage with the collecting element.

2. A vacuum tube amplifier, comprising an evacuated envelope, aplurality of stages contained therein, a single filament common to allthe stages, a control electrode and a plate electrode for each stage, ablocking condenser between each grid and the plate of the precedingstage, a conducting element within the tube, a high resistance elementconnecting each plate with said conducting element, all of said elementsmounted entirely within the tube, and external leads for the filament,conductor, first control electrode and the last plate.

3. A vacuum tube adapted for multi-stage amplification, comprising anevacuated envelope, a plurality of stages contained therein, a controlelectrode and a plate electrode for each stage and a common filament forall the stages, a bus adapted to supply positive potential to theplates, a high resistance element connecting each plate with said bus, acondenser connecting each grid with the plate of the preceding stage, abus adapted to supply negative potential, a high resistance elementconnecting the control electrode of the last stage with the said lastnamed bus, all of said elements being mounted entirely w thin the tube,and external leads for the filament, first control electrode, last plateand said buses.

4. A multistage vacuum tube amplifier, comprising an evacuated envelope;a plurality of resistance-coupled stages wholly contained Within saidenvelope, at common cathode for all said stages, grid and plateelectrodes for each of the stages, external con- 7 necti'ons to bothterminals of the-common cathode, an externaliconnection tothe gridelectrode of the first stage, another external 7 connection common tothe grid electrodes of thesucceeding stages, an external connection tothe'plate electrode of the last stage, and

another external connection common to the plate electrodes of theremaining stages.

In testimony whereof I have affixed my signaturel SIEGMUND LOEWE.

at L.

